tkinter: afterメソッドを1ミリ秒以下にできたが、機序が分からない

# -*- coding: utf-8 -*-
import tkinter as tk
import math
import time
import random

# キャンバスのサイズの設定
CANVAS_WIDTH = 400
CANVAS_HEIGHT = CANVAS_WIDTH
CANVAS_SIZE = CANVAS_WIDTH

# 時計の前面と背景の色の設定
BG_COLOR = "black"

#時計の外枠
FG_COLOR = "gray"

# 盤面を表す円の半径の設定
CLOCK_OVAL_RADIUS = CANVAS_SIZE / 2

#針の長さ
R = CLOCK_OVAL_RADIUS*0.95

# キャンバスの中心座標
X0 = CANVAS_HEIGHT/2
Y0 = CANVAS_WIDTH/2

class POV(tk.Frame):
    def __init__(self, master=None):
        super().__init__(master)
  
        self.frame0= tk.Frame(self.master, bg="white") 
        self.frame0.pack()  
        
        # 変数定義
        self.rad =0
        self.after_id = 0    
        self.time_lst = [0,]
    
        self.create_widget()
        self.create_button()
        self.draw_hand()
        
    def create_widget(self):
        self.canvas = tk.Canvas(self.frame0, width = CANVAS_WIDTH, height = CANVAS_HEIGHT, 
                                     bg=BG_COLOR, highlightthickness=0)
        #gridは3x3       
        self.canvas.grid(column=0, row=0, columnspan=3, padx=0, pady=0,
                         sticky=tk.NSEW,
                         )  

        # 時計の盤面を表す円を描画する
        x1 = X0 - CLOCK_OVAL_RADIUS
        y1 = Y0 - CLOCK_OVAL_RADIUS
        x2 = X0+ CLOCK_OVAL_RADIUS
        y2 = Y0+ CLOCK_OVAL_RADIUS

        self.canvas.create_oval(
            x1, y1, x2, y2,
            fill="black",
            width=2,
            outline="gold"
        )

    def draw_hand(self):
        self.hand1 = self.canvas.create_line(
        X0, Y0, X0+R*math.cos(self.rad), Y0+R*math.sin(self.rad),
            fill="white",
            width=10,
        )        
        # math.pi/180が1度なので、3度ずらした針
        self.hand2 = self.canvas.create_line(
        X0, Y0, X0+R*math.cos(self.rad+ 3*math.pi/180), Y0+R*math.sin(self.rad+3*math.pi/180),
            fill="white",
            width=10,
        ) 
                
    def rotate_hand(self):
        #ループの間隔測定
        time_a = time.time()
        duration = time_a - self.time_lst[-1]
        self.time_lst.append(time_a)
        dur_r = round(duration, 5)
        
        #print頻度を調整
        r = random.randint(1, 300)
        if r ==5:
            print(dur_r)
        
        xr = X0+R*math.cos(self.rad)
        yr = Y0+R*math.sin(self.rad)
        
        xr_2 = X0+R*math.cos(self.rad+3*math.pi/180)
        yr_2 = Y0+R*math.sin(self.rad+3*math.pi/180)       
        
        self.canvas.coords(self.hand1, X0, Y0, xr, yr)
        self.canvas.coords(self.hand2, X0, Y0, xr_2, yr_2)
        
        #1度ずつふえる
        if self.rad > 2*math.pi:
            self.rad = self.rad -  2*math.pi
        
        self.rad += math.pi/180
        self.after_id = self.after(1, self.rotate_hand)

    def create_button(self):
        self.start_button = tk.Button(self.frame0, width=20, height=1, text="開始", fg = "gray20",
                                 font=("MSゴシック体", "14"), command=self.start_button_clicked)
        self.start_button.grid(column=0, row=1, columnspan=3, sticky=tk.NSEW)
              
        self.stop_button = tk.Button(self.frame0, width=20, height=1, text="停止", fg = "gray20",
                                 font=("MSゴシック体", "14"), command=self.stop_button_clicked)
        self.stop_button.grid(column=0, row=2, columnspan=3, sticky=tk.NSEW)
    
    #ボタンを押した時
    def start_button_clicked(self):
            self.rotate_hand()
            
    def stop_button_clicked(self):
            self.after_cancel(self.after_id)

if __name__ == "__main__":
    app = tk.Tk()
    POV(app)
    app.mainloop()